| 1. |
- Anand, S, et al.
(författare)
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Divergence of Hoxc8 early enhancer parallels diverged axial morphologies between mammals and fishes
- 2003
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 100:26, s. 15666-15669
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Tidskriftsartikel (refereegranskat)abstract
- There is considerable interest in understanding how cis-regulatory modifications drive morphological changes across species. Because developmental regulatory genes, including Hox genes, are remarkably conserved, their noncoding regulatory regions are likely sources for variations. Modifications of Hox cis-regulatory elements have potential to alter Hox gene expression and, hence, axial morphologies. In vertebrates, differences in the axial levels of Hox gene expression correlate with differences in the number and relative position of thoracic vertebrae. Variation in cis-regulatory elements of Hox genes can be identified by comparative sequence and reporter gene analyses in transgenic mouse embryos. Using these approaches, we show a remarkable divergence of the Hoxc8 early enhancers between mammals and fishes representing diverse axial morphologies. Extensive restructuring of the Hoxc8 early enhancer including nucleotide substitutions, inversion, and divergence result in distinct patterns of reporter gene expression along the embryonic axis. Our results provide an evolutionary perspective on how the enhancer elements are engineered and support the hypothesis that remodeling of Hox regulatory elements in different species has played a significant role in generating morphological diversity.
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| 2. |
- Chu, H.S., et al.
(författare)
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Discovery of Helical Magnetic Fields in AGN and CME and Ejection of Large Scale Magnetic Fields from AGN
- 2003
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Ingår i: Symposium - International astronomical union. - : International Astronomical Union. - 0074-1809. ; 214, s. 303-310
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic Fields are the crucial and most important ingredient involved in the processes of various violent activities in Active Galactic Nuclei and other celestial bodies. The generally accepted 2-sided symmetric-jets model of active galactic nuclei (AGN) does not include the magnetic fields. We present here the first direct detection of helical magnetic field in AGN, and the first direct detection of ejection of large scale magnetic fields from AGN. (CME) 2. The annular (helical) magnetic field is responsible for the collimation of the jet (through Pinch Effect) and may be of crucial importance for extraction of black hole rotational energy. 3. The CMEs are responsible for sporadic ejection of jet components in AGN, while the general accepted 2-sided jets pertain to the quiescent Jets. 4.Observations show that the CME with Asymmetric Jets can explain many phenomena and much of the morphological diversities in AGN.
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| 3. |
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| 4. |
- Digham, F, et al.
(författare)
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Joint Pilot and Data Loading Technique for MIMO Systems Operating with Covariance Feedback
- 2004
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Ingår i: Fifth IEE International Conference on 3G Mobile Communication Technologies, 2004. 3G 2004.. - 0863413889 ; , s. 24-28
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Konferensbidrag (refereegranskat)abstract
- We consider a multiple input multiple output (MIMO) system wherein channel correlation as well as noisy channel estimation are both taken into account. For a given block fading duration, pilot-assisted channel estimation is carried out with the aid of a minimum mean square error estimator. The pilot sequences and data are jointly optimized to maximize the ergodic capacity while fulfilling a total transmit energy constraint. Using the optimization results, we study the effect of various system parameters and different types of channel knowledge. We show that systems with channel covariance knowledge and imperfect channel estimates can even outperform those with perfect channel estimation at the receiver, but without any channel knowledge at the transmitter. Further, we show that the signal to noise ratio and the block fading duration determine the qualitative behavior of ergodic capacity as a function of antenna spacing or angular spread. Finally, we find that the optimum pilot-to-data power ratio is always greater than one. It increases as the total transmit power decreases or as the block fading length increases.
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| 5. |
- Du, J, et al.
(författare)
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Estimation of Performance Loss Due to Delay in Channel Feedback in MIMO Systems
- 2004
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Ingår i: 2004 IEEE 60th Vehicular Technology Conference, 2004. VTC2004-Fall.. - 0780385217 ; 3, s. 1619-1622
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Konferensbidrag (refereegranskat)abstract
- Latency of available channel state information (CSI) at the transmitter in time-varying channels greatly affects the performance of multiple-input multiple-output (MIMO) systems. We have derived a simple algorithm to calculate an approximation of the expected performance loss based on the most recent channel feedback. The proposed algorithm can be used to determine the maximum tolerable channel feedback delay for each particular channel realization.
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| 6. |
- Ellison, A., et al.
(författare)
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Epitaxial growth of SiC in a chimney CVD reactor
- 2002
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 236:1-3, s. 225-238
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Tidskriftsartikel (refereegranskat)abstract
- A high growth rate (>10 µm/h) Chemical Vapour Deposition (CVD) process is investigated in a vertical hot-wall, or "chimney", reactor. By the use of increased temperatures (1650-1850°C) and concentrations of reactants, this process is shown to enable growth rates up to 50µm/h and demonstrates a material quality comparable to established CVD techniques until growth rates of 25 µm/h. The gas flow dynamics, the growth rate and the thickness uniformity determining steps are investigated, and the role of homogenous nucleation is analysed. The growth rate is shown to be influenced by two competing processes: the supply of growth species and the etching of the hydrogen carrier gas. The exponential increase of the growth rate with temperature is related to a Si-vapour release from clusters homogeneously nucleated in the inlet of the susceptor and acting as a growth species reservoir. © 2002 Elsevier Science B.V. All rights reserved.
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| 7. |
- Ellison, A, et al.
(författare)
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Fast SiC epitaxial growth in a chimney CVD reactor and HTCVD crystal growth developments
- 2000
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Ingår i: Materials science Forum, Vols. 338-342. - : Trans Tech Publications Inc.. - 0878498540 ; , s. 131-136
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Konferensbidrag (refereegranskat)abstract
- The epitaxial growth of SiC is investigated in a CVD process based on a vertical hot-wall, or "chimney", reactor geometry. Carried out at increased temperatures (1650 to 1850 degreesC) and concentrations of reactants, the growth process enables epitaxial rates ranging from 10 to 50 mum/h. The growth rate is shown to be influenced by two competing processes: the supply of growth species in the presence of homogeneous gas-phase nucleation, and, the etching effect of the hydrogen carrier gas. The quality of thick (20 to 100 mum) low-doped 4H-SiC epitaxial layers grown at rates ranging between 10 and 25 mum/h are discussed in terms of thickness uniformity, surface morphology and purity. The feasibility of high voltage Schottky rectifiers (V-BR from 2 to similar to3.8 kV) on as-grown chimney CVD epilayers is reported. In a second part, recent developments of the High Temperature Chemical Vapor Deposition (HTCVD) technique for SiC crystal growth are described. Using pure gases (SiH4 and C2H4) as source material and growth temperatures of 2100-2300 degreesC, this technique enables at present growth rates ranging from 0.4 to 0.8 mm/h. 6H and 4H-SiC crystals of thickness up to 7 mm and diameters up to 40 mm have been grown. We report micropipe densities of similar to 80 cm(-2) over areas of 0.5 cm(2) in 35 mm diameter 4H-SiC wafers sliced from HTCVD grown crystals. Undoped wafer demonstrators exhibit semi-insulating behavior with a bulk resistivity higher than 7.10(9) Omega cm at room temperature.
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| 8. |
- Eriksson, S, et al.
(författare)
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Complex formation of myrosinase isoenzymes in Brassica napus seeds are dependent on the presence of myrosinase binding proteins
- 2002
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Ingår i: Plant Physiology. - 1532-2548. ; 129:4, s. 1592-1599
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme myrosinase (EC 3.2.3.1) degrades the secondary compounds glucosinolates upon wounding and serves as a defense to generalist pests in Capparales. Certain myrosinases are present in complexes together with other proteins such as myrosinase-binding proteins (MBP) in extracts of oilseed rape (Brassica napus) seeds. Immunhistochemical analysis of wild-type seeds showed that MBPs were present in most cells but not in the myrosin cells, indicating that the complex formation observed in extracts is initiated upon tissue disruption. To study the role of MBP in complex formation and defense, oilseed rape antisense plants lacking the seed MBPs were produced. Western blotting and immunohistochemical staining confirmed depletion of MBP in the transgenic seeds. The exclusive expression of myrosinase in idioblasts (myrosin cells) of the seed was not affected by the down-regulation of MBP. Using size-exclusion chromatography, we have shown that myrosinases with subunit molecular masses of 62 to 70 kD were present as free dimers from the antisense seed extract, whereas in the wild type, they formed complexes. In accordance with this, MBPs are necessary for myrosinase complex formation of the 62- to 70-kD myrosinases. The product formed from sinalbin hydrolysis by myrosinase was the same whether MBP was present or not. The performance of a common beetle generalist (Tenebrio molitor) fed with seeds, herbivory by flea beetles (Phyllotreta undulata) on cotyledons, or growth rate of the Brassica fungal pathogens Alternaria brassicae or Lepthosphaeria maculans in the presence of seed extracts were not affected by the down-regulation of MBP, leaving the physiological function of this protein family open.
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| 9. |
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| 10. |
- Ivanov, Ivan Gueorguiev, et al.
(författare)
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Intrinsic photoconductivity of 6H-SiC and the free-exciton binding energy
- 2001
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Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 405-408
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Konferensbidrag (refereegranskat)abstract
- The paper presents a study of the low-temperature photoconductivity of 6H-SiC. The photocurrent at the absorption edge is assigned to Auger recombination of excitons captured to impurities. This is shown to saturate and decrease with increasing the photon energy, so the further increase in the photocurrent, observed in the purest sample, can be attributed to free excitons created in non-bound states in the exciton continuum. Thus, the exciton binding energy can be estimated, E-bx approximate to 60 +/- 5 meV in 6H-SiC.
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